Diesel engines normally operate by flowing air into each cylinder during the intake stroke, and compressing the air to a high temperature during the compression stroke. At the end of the compression stroke, fuel is injected into the compressed and heated air, and it immediately ignites to produce high pressures that are used during the subsequent power stroke. During the very short time between injection of fuel and an early portion of the power stroke, there is poor mixing of fuel and air. This results in incomplete burning of fuel and consequent unburned hydrocarbons, leading to a reduction of efficiency and an increase in pollution components that must be removed or which contaminate the environment. In an ignition engine, a critical mixture of fuel and air is flowed into each cylinder during the intake stroke, or air is flowed in and fuel is injected, with a spark applied at the top of the compression stroke to produce power. In both cases, the air-fuel ratio should be between about 7 and 18 at moderate to full load to assure that the mixture will burn, either when fuel is injected or when a spark is applied.
In a diesel engine, the compression ratio is between about 12:1 and 22:1, with almost all diesel engines for vehicles using a ratio of about 16:1 to 18:1. In spark ignition engines, the compression ratio is between 6:1 and 12:1, with almost all spark ignition engines used on automobiles having a compression ratio of about 7.5:1 to 8.5:1. While the much higher compression ratio of a diesel engine results in greater efficiency, the increase in unburned hydrocarbons and resulting pollution is a major disadvantage of diesel engines. If the amount of unburned hydrocarbons in diesel engines could be reduced, this would significantly increase the acceptability of such engines.
In accordance with one embodiment of the present invention, an engine with a high compression ratio is provided wherein fuel and air are more throughly mixed for better efficiency and lower pollution. The engine has a compression ratio of at least 12:1 which is typical for diesel engines. Instead of flowing only air into each cylinder during the intake stroke, applicant supplies a subcritical mixture of finely atomized fuel in air into each cylinder. The subcritical mixture has an air-fuel ratio such as more than 18:1, so it will not ignite when heated to the high temperature achieved near the-end of the compression stroke. However, near the end of the compression stroke, fuel is injected into the hot, compressed and lean air-fuel mixture to create a critical mixture that immediately ignites to produce high pressure gasses for the power stroke.
The air-fuel mixture that is admitted into each cylinder during the intake stroke preferably contains more than half the fuel that is consumed in each cycle of operation. Although each stroke of the piston may use almost the same total amount of fuel as a present diesel engine, much of the fuel is atomized and well mixed with the air at the time that additional fuel is injected and ignition occurs. The fuel that was originally introduced during the intake stroke will burn substantially completely and cleanly, resulting in a higher percentage of the fuel being burned. This results in greater efficiency and a lower percent discharge of unburned fuel particles.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.